Power converters are becoming increasingly important in the high-tech industry. Customers are demanding increased functionality, such as differing voltage levels, higher currents, faster response times, etc. Some examples of power converters include power supplies for computer peripherals, disk drives, video game consoles, etc.
New standards for delivering power, such as Universal Serial Bus (USB) type-C, can allow for adaptable power levels. For example, devices can negotiate increased USB current through a configuration line. However, the USB specification requires that the negotiated power must be reached in 265 ms.
FIG. 1 shows a portion of a power supply compatible with USB type-C. A communications line 110 can be used to negotiate an adaptable voltage level (e.g., 5V or 20V). A micro-control unit (MCU) 120 reads the communications line 110 to determine if a request for a voltage change from high to low occurred. If so, the MCU turns on a discharge Field Effect Transistor (FET) 130 so as to discharge a power supply capacitor 140 through a resistor 150. A synchronous rectifier 160 controls a sync FET 170 and ensures that a flyback current does not pass through a transformer 180. Generally, the current flows from the transformer 180 through the sync FET 170 to charge the capacitor 140. However, the flyback current flows in the opposite direction, sometimes due to voltage spikes or other anomalies. The synchronous rectifier 160 can monitor a voltage level on a secondary winding of the transformer 180 and deactivate the sync FET 170 accordingly so as to prevent any flyback currents from occurring.
There are several problems with such a solution. First, there are multiple components needed, such as the discharge FET 130 and the resistor 150. Second, when switching from 20V to 5V in 265 ms, the current through the resistor 150 is dissipated in the circuit as heat, which is wasteful and potentially hurtful to the operation of the power supply.
Thus, there is a need for a more efficient adaptable power supply.